U.S. patent application number 14/446930 was filed with the patent office on 2015-07-23 for bicycle sprocket.
The applicant listed for this patent is Shimano Inc.. Invention is credited to Mitsuru KAMIYA, Yusuke NISHIMOTO.
Application Number | 20150203173 14/446930 |
Document ID | / |
Family ID | 53544121 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203173 |
Kind Code |
A1 |
NISHIMOTO; Yusuke ; et
al. |
July 23, 2015 |
BICYCLE SPROCKET
Abstract
A sprocket is engageable with a chain having rollers. The
sprocket includes a body and a tooth portion. The tooth portion has
front and rear surfaces, a drive side surface and a non-drive side
surface. The rear and front surfaces face in opposite axial
directions. The drive side surface axially connects the front and
rear surfaces on a downstream side. The non-drive side surface
axially connects the front and rear surfaces on an upstream side.
One of the front and rear surfaces has a first chamfered portion,
which is formed in a radially outer portion of at least one tooth
portion and tapered radially outward in the axial direction. The
drive side surface has a first protrusion, which protrudes
downstream in the drive rotation direction and is located radially
outwardly from a contact position where the drive side surface
contacts each of the rollers when the chain is driven.
Inventors: |
NISHIMOTO; Yusuke; (Osaka,
JP) ; KAMIYA; Mitsuru; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shimano Inc. |
Osaka |
|
JP |
|
|
Family ID: |
53544121 |
Appl. No.: |
14/446930 |
Filed: |
July 30, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61930542 |
Jan 23, 2014 |
|
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Current U.S.
Class: |
474/152 |
Current CPC
Class: |
B62M 2009/007 20130101;
B62M 9/02 20130101 |
International
Class: |
B62M 9/02 20060101
B62M009/02 |
Claims
1. A bicycle sprocket engageable with a chain having rollers, the
sprocket comprising: a body rotatable around a center rotational
axis; and at least one tooth portion provided along a peripheral
portion of the body, and having a front surface, a rear surface
that faces away from the front surface in an axial direction of the
center rotational axis, a drive side surface that connects the
front and rear surfaces to each other in the axial direction on a
downstream side with respect to a drive rotation direction, and
anon-drive side surface that connects the front and rear surfaces
to each other in the axial direction on an upstream side with
respect to the drive rotation direction, the at least one tooth
portion being configured such that one of the front and rear
surfaces has a first chamfered portion that is formed in a radially
outer portion of the at least one tooth portion and tapered
radially outward in the axial direction, and the drive side surface
has a first protrusion that protrudes downstream in the drive
rotation direction and located radially outwardly from a contact
position where the drive side surface comes into contact with each
of the rollers when the chain is driven.
2. The bicycle sprocket according to claim 1, wherein the first
protrusion protrudes downstream in the drive rotation direction
from the contact position, where the drive side surface comes into
contact with each of the rollers when the chain is driven, by a
first distance that is greater than or equal to 0.1 mm but smaller
than or equal to 0.5 mm.
3. The bicycle sprocket according to claim 2, wherein the first
distance is greater than or equal to 0.2 mm but smaller than or
equal to 0.3 mm.
4. The bicycle sprocket according to claim 2, wherein the first
distance is 0.2 mm.
5. The bicycle sprocket according to claim 1, wherein the non-drive
side surface has a raised portion that is convex in a
circumferential direction toward the upstream side with respect to
the drive rotation direction, and the raised portion protrudes by
an amount that is smaller than an amount that the first protrusion
protrudes.
6. The bicycle sprocket according to claim 1, wherein the non-drive
side surface has a second protrusion that protrudes in a
circumferential direction.
7. The bicycle sprocket according to claim 1, wherein the tooth
portion has a first tooth, a second tooth and a third tooth, the
second tooth being adjacent the first tooth and upstream of the
first tooth in the drive rotation direction, the third tooth being
adjacent the second tooth and upstream of the second tooth in the
drive rotation direction, and a contact position where each of the
rollers contacts the drive side surface of the first tooth when the
chain is driven is spaced from a tip downstream position that is a
position of a tip of the third tooth on a most downstream side with
respect to the drive rotation direction by a second distance that
is greater than or equal to 25.4 mm but smaller than or equal to 27
mm.
8. The bicycle sprocket according to claim 7, wherein the second
distance is greater than or equal to 25.4 mm but smaller than or
equal to 26.6 mm.
9. The bicycle sprocket according to claim 1, wherein the other one
of the front surface and the rear surface has a second chamfered
portion that is formed in a radially outer portion of the at least
one tooth portion and tapered radially outward in the axial
direction.
10. The bicycle sprocket according to claim 9, wherein the front
surface has the first chamfered portion, and the rear surface has
the second chamfered portion.
11. The bicycle sprocket according to claim 10, wherein a radial
outer periphery end of the first chamfered portion is spaced from a
radial inner periphery end of the first chamfered portion by a
third distance in the axial direction, and a radial outer periphery
end of the second chamfered portion is spaced from a radial inner
periphery end of the second chamfered portion by a fourth distance
in the axial direction, and the fourth distance is equal to the
third distance.
12. The bicycle sprocket according to claim 10, wherein a radial
outer periphery end of the first chamfered portion is spaced from a
radial inner periphery end of the first chamfered portion by a
third distance in the axial direction, and a radial outer periphery
end of the second chamfered portion is spaced from a radial inner
periphery end of the second chamfered portion by a fourth distance
in the axial direction, and the fourth distance differs from the
third distance.
13. The bicycle sprocket according to claim 12, wherein the third
distance is greater than the fourth distance.
14. The bicycle sprocket according to claim 1, wherein the tooth
portion includes at least one group of a plurality of first teeth
and at least one group of a plurality of second teeth, each of the
first teeth having a first chain engagement thickness in the axial
direction, each of the second teeth having a second chain
engagement thickness in the axial direction, and the second chain
engagement thickness is greater than the first chain engagement
thickness, and the total number of teeth in the tooth portion is an
even number.
15. The bicycle sprocket according to claim 14, wherein the first
chain engagement thickness of each of the first teeth is a
thickness that allows engagement with inner link plates of the
chain but does not allow engagement with outer link plates, and the
second chain engagement thickness of each of the second teeth is a
thickness that allows engagement with outer link plates of the
chain.
16. The bicycle sprocket according to claim 15, wherein each of the
groups of the first teeth and each of the groups of the second
teeth are alternately arranged in a circumferential direction.
17. The bicycle sprocket according to claim 1, wherein the tooth
portion is formed of a stacked member including three layers
stacked on each other in the axial direction.
18. The bicycle sprocket according to claim 17, wherein the stacked
member includes a first member made of a first metallic material, a
second member made of a second metallic material, and a third
member disposed between the first member and the second member in
the axial direction and made of a third metallic material, and a
specific gravity of the third metallic material is smaller than a
specific gravity of each of the first and second metallic
materials.
19. The bicycle sprocket according to claim 18, wherein each of the
first and second metallic materials is iron, and the third metallic
material is aluminum.
20. The bicycle sprocket according to claim 17, wherein the stacked
member includes a first member made of a first metallic material, a
second member made of a second metallic material, and a third
member disposed between the first member and the second member in
the axial direction and made of a non-metallic material.
21. The bicycle sprocket according to claim 20, wherein the
non-metallic material contains a resin.
22. The bicycle sprocket according to claim 1, wherein a straight
line that connects a contact position where each of the rollers
comes into contact with the drive side surface when the chain is
driven to the center rotational axis and a line tangential to the
drive side surface in the contact position form an angle smaller
than or equal to 7 degrees.
23. The bicycle sprocket according to claim 22, wherein the angle
is smaller than or equal to 3 degrees.
24. A bicycle sprocket engageable with a chain having rollers, the
sprocket comprising: a body rotatable around a center rotational
axis; and at least one tooth portion provided along a peripheral
portion of the body, and having a front surface, a rear surface
that faces away from the front surface in an axial direction of the
center rotational axis, a drive side surface that connects the
front and rear surfaces to each other in the axial direction on a
downstream side with respect to a drive rotation direction, and a
non-drive side surface that connects the front and rear surfaces to
each other in the axial direction on an upstream side with respect
to the drive rotation direction, the at least one tooth portion
being configured such that one of the front and rear surfaces has a
first chamfered portion that is formed in a radially outer portion
of the at least one tooth portion and tapered radially outward in
the axial direction, and a straight line that connects a contact
position where each of the rollers comes into contact with the
drive side surface when the chain is driven to the center
rotational axis and a line tangential to the drive side surface in
the contact position form an angle smatter than or equal to 7
degrees.
25. The bicycle sprocket according to claim 24, wherein the angle
is smaller than or equal to 3 degrees.
26. The bicycle sprocket according to claim 24, wherein the tooth
portion has a first tooth, a second tooth and a third tooth, the
second tooth being adjacent the first tooth and upstream of the
first tooth in the drive rotation direction, the third tooth being
adjacent the second tooth and upstream of the second tooth in the
drive rotation direction, and a contact position where each of the
rollers contacts the drive side surface of the first tooth when the
chain is driven is spaced from a tip downstream position that is a
position of a tip of the third tooth on a most downstream side with
respect to the drive rotation direction by a second distance that
is greater than or equal to 25.4 mm but smaller than or equal to 27
mm.
27. The bicycle sprocket according to claim 26, wherein the second
distance is greater than or equal to 25.4 mm but smaller than or
equal to 26.6 mm.
28. The bicycle sprocket according to claim 24, wherein the other
one of the front surface and the rear surface has a second
chamfered portion that is formed in a radially outer portion of the
at least one tooth portion and tapered radially outward in the
axial direction.
29. The bicycle sprocket according to claim 28, wherein the front
surface has the first chamfered portion, and the rear surface has
the second chamfered portion.
30. The bicycle sprocket according to claim 29, wherein a radial
outer periphery end of the first chamfered portion is spaced from a
radial inner periphery end of the first chamfered portion by a
third distance in the axial direction, and a radial outer periphery
end of the second chamfered portion is spaced from a radial inner
periphery end of the second chamfered portion by a fourth distance
in the axial direction, and the fourth distance differs from the
third distance.
31. The bicycle sprocket according to claim 29, wherein the third
distance is greater than the fourth distance.
32. The bicycle sprocket according to claim 24, wherein the third
distance is greater than or equal to 0.9 mm but smaller than or
equal to 1.1 mm, and the fourth distance is greater than or equal
to 0.6 mm but smaller than or equal to 0.9 mm.
33. The bicycle sprocket according to claim 24, wherein the tooth
portion includes a group of a plurality of first teeth and a group
of a plurality of second teeth, each of the first teeth haying a
first chain engagement thickness in the axial direction, each of
the second teeth having a second chain engagement thickness in the
axial direction, and the second chain engagement thickness is
greater than the first chain engagement thickness, and the total
number of teeth in the tooth portion is an even number.
34. The bicycle sprocket according to claim 33, wherein the first
chain engagement thickness of each of the first teeth is a
thickness that allows engagement with inner link plates of the
chain but does not allow engagement with outer link plates, and the
second chain engagement thickness of each of the second teeth is a
thickness that allows engagement with the outer link plates of the
chain.
35. The bicycle sprocket according to claim 34, wherein each of the
groups of the first teeth and each of the groups of the second
teeth are alternately arranged in a circumferential direction.
36. The bicycle sprocket according to claim 24, wherein the tooth
portion is formed of a stacked member including three layers
stacked on each other in the axial direction.
37. The bicycle sprocket according to claim 36, wherein the stacked
member includes a first member made of a first metallic material, a
second member made of a second metallic material, and a third
member made of a third metallic material, and a specific gravity of
the third metallic material is smaller than a specific gravity of
each of the first and second metallic materials.
38. The bicycle sprocket according to claim 37, wherein each of the
first and second metallic materials is iron, and the third metallic
material is aluminum.
39. The bicycle sprocket according to claim 38, wherein the stacked
member includes a first member made of a first metallic material, a
second member made of a second metallic material, and a third
member made of a non-metallic material.
40. The bicycle sprocket according to claim 39, wherein the
non-metallic material contains a resin.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/930,542, filed on Jan. 23, 2014. The entire
disclosure of U.S. Provisional Application No. 61/930,542 is hereby
incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a sprocket. In
particular, the present invention relates to a bicycle sprocket
engageable with a chain having rollers.
[0004] 2. Background Information
[0005] in a bicycle provided with a plurality of rear sprockets,
speed change is performed by using a rear derailleur. When a rider
on such a bicycle travels on a rough terrain, irregularities on the
terrain cause the chain guide of the rear derailleur to vibrate
like a pendulum, which changes the tension acting on the chain. It
is preferable that a change in the tension acting on the chain is
unlikely to result in disengagement of the chain from the
front-side sprocket.
[0006] US 2013/0139642A1 discloses a sprocket having a plurality of
first teeth and the same number of second teeth longer than the
first teeth in the direction of the axis of rotation of the
sprocket, that is, thicker than the first teeth with the first and
second teeth alternately arranged. In this configuration, the first
teeth engage with narrow-inner-width inner link plates of the
chain, and the second teeth engage with wide-inner-width inner link
plates of the chain, resulting in an increased chain holding force,
whereby the chain is unlikely to disengage from the sprocket during
travel on a rough road. Further, in the sprocket of the related
art, a side surface on the upstream side in the direction in which
the sprocket is driven and rotated, that is, a non-drive side
surface with which the rollers of the chain do not come into
contact has a shape that protrudes in the circumferential
direction. The shape further increases the chain holding force.
SUMMARY
[0007] The sprocket of the related art, which has the first and
second teeth having thicknesses different from each other and
alternately arranged, provides an increased chain holding force.
The idea of different thicknesses is applicable only to a sprocket
having an even total number of teeth but is not applicable to a
sprocket having an odd total number of teeth.
[0008] An object of the invention is provide a bicycle sprocket
providing an increased chain holding force (that is, force based on
which sprocket holds chain) without alternately differentiating the
thickness of tooth portions of the sprocket.
[0009] A bicycle sprocket according to an aspect of the invention
is engageable with a chain having rollers. The bicycle sprocket
includes a body and at least one tooth portion. The body is
rotatable around a center rotational axis. The at least one tooth
portion is provided along a peripheral portion of the body and has
a front surface, a rear surface that faces away from the front
surface in an axial direction of the center rotational axis, a
drive side surface that connects the front and rear surfaces to
each other in the axial direction on a downstream side with respect
to a drive rotation direction, and anon-drive side surface that
connects the front and rear surfaces to each other in the axial
direction on an upstream side with respect to the drive rotation
direction.
[0010] The at least one tooth portion has a first chamfered portion
in a radially outer portion of one of the front surface and the
rear surface, and the first chamfered portion is so formed that it
is tapered radially outward in the axial direction. The drive side
surface has a first protrusion that protrudes downstream in the
drive rotation direction and located in a radially outwardly from a
contact position where the drive side surface comes into contact
with each of the rollers when the chain is driven.
[0011] In the sprocket, the first protrusion, which protrudes
downward in the drive rotation direction, is provided radially
outwardly from a position where the roller comes into contact with
the drive side surface. The first protrusion therefore restricts
movement of each of the rollers of the chain that comes into
contact with the drive side surface, whereby the roller is unlikely
to move radially outward. The configuration described above allows
an increase in the chain holding force without alternately
differentiating the axial thickness of the plurality of tooth
portions. Both a sprocket having an even total number of teeth and
a sprocket having an odd total number of teeth can therefore
provide an increased chain holding force, Further, since one of the
front surface and the rear surface has the first chamfered portion
tapered and formed in a radially outer portion of the at least one
tooth portion, the sprocket that rotates in the drive rotation
direction can readily engage with the chain even when the first
protrusion is provided to improve the chain holding force.
[0012] The first protrusion protrudes downstream in the drive
rotation direction from the contact position, where the drive side
surface conies into contact with each of the rollers when the chain
is driven, by a first distance that is greater than or equal to 0.1
mm but smaller than or equal to 0.5 mm. The configuration allows
the tooth portion of the sprocket to readily engage with the chain
and prevents the chain that engages with the sprocket from readily
disengaging from the sprocket.
[0013] The first distance may be greater than or equal to 0.2 mm
but smaller than or equal to 0.3 mm.
[0014] The first distance may be 0.2 mm.
[0015] The non-drive side surface has a raised portion that is
convex in a circumferential direction toward the upstream side with
respect to the drive rotation direction, and the raised portion
protrudes by an amount that is smaller than an amount that the
first protrusion protrudes, In this case, providing the raised
portion maintains ease of engagement between the tooth portion and
the chain and effectively prevents the chain from disengaging from
the tooth portion.
[0016] The non-drive side surface may have a second protrusion that
protrudes in a circumferential direction. Providing the second
protrusion restricts radially outward movement of each of the
rollers also on the non-drive surface, whereby the chain holding
force is further increased.
[0017] The tooth portion may have tooth portion has a first tooth,
a second tooth and a third tooth, the second tooth being adjacent
the first tooth and upstream of the first tooth in the drive
rotation direction, the third tooth being adjacent the second tooth
and upstream of the second tooth in the drive rotation direction,
and a contact position where each of the rollers contacts the drive
side surface of the first tooth when the chain is driven is spaced
from a tip downstream position that is a position of a tip of the
third tooth on a most downstream side with respect to the drive
rotation direction by a second distance that is greater than or
equal to 25.4 mm but smaller than or equal to 27 mm.
[0018] In this case, a threshold distance that is a reference used
to determine whether or not the third tooth of the rotating
sprocket engages with the chain (distance between first tooth and
third tooth) is at least twice the intervals between the rollers of
the chain (typically 12.7 mm), whereby the chain is readily caught
in a reliable manner.
[0019] The second distance may be greater than or equal to 25.4 mm
but smaller than or equal to 26.6 mm.
[0020] The other one of the front surface and the rear surface may
have a second chamfered portion that is formed in a radially outer
portion of the at least one tooth portion and tapered radially
outward in the axial direction. In this case, since a chamfered
portion is provided on each of the front and rear surfaces, the
chain further readily engage with the tooth portion of the
sprocket.
[0021] The front surface may have the first chamfered portion, and
the rear surface may have the second chamfered portion.
[0022] A radial outer periphery end of the first chamfered portion
is spaced from a radial inner periphery end of the first chamfered
portion by a third distance in the axial direction, and a radial
outer periphery end of the second chamfered portion is spaced from
a radial inner periphery end of the second chamfered portion by a
fourth distance in the axial direction that is equal to the third
distance. In this case, since the axial distances of the first
chamfered portion and the second chamfered portion are equal to
each other, the chain is unlikely to disengage from the tooth
portion even when the chain vibrates in the axial direction.
[0023] A radial outer periphery end of the first chamfered portion
is spaced from a radial inner periphery end of the first chamfered
portion by a third distance in the axial direction, and a radial
outer periphery end of the second chamfered portion is spaced from
a radial inner periphery end of the second chamfered portion by a
fourth distance in the axial direction that differs from the third
distance.
[0024] The third distance may be greater than the fourth
distance.
[0025] In this case, since the first chamfered portion formed in
the front surface of the sprocket is deeper than the second
chamfered portion formed in the rear surface of the sprocket, the
extreme tip of the tooth portion of the sprocket is positioned
closer to the rear surface. When the sprocket according to the
invention is a front sprocket, and the chain is so set from the
rear sprocket toward the front sprocket that the chain is inclined
obliquely outward in the axial direction, the chain readily engages
with the front sprocket.
[0026] The tooth portion includes a group of a plurality of first
teeth and a group of a plurality of second teeth, each of the first
teeth having a first chain engagement thickness in the axial
direction, each of the second teeth having a second chain
engagement thickness in the axial direction that is greater than
the first thickness, and the total number of teeth in the tooth
portion is an even number. In this case, the thickness of each of
the first teeth is set in accordance with the gap between a pair of
inner links of the chain, and the thickness of each of the second
teeth is set in accordance with the gap between a pair of outer
links of the chain, whereby the chain holding force is further
increased.
[0027] The first chain engagement thickness of each of the first
teeth may be a thickness that allows engagement with inner link
plates of the chain, and the second chain engagement thickness of
each of the second teeth may be a thickness that allows engagement
with outer link plates of the chain.
[0028] The group of first teeth and the group of second teeth may
be alternately arranged in a circumferential direction.
[0029] The tooth portion may be formed of a stacked member
including three layers stacked on each other in the axial
direction. In this case, using a light material to form the
intermediate layer of the stacked member, which does not come into
contact with the chain, allows the weight of the sprocket to be
reduced.
[0030] The stacked member may include a first member made of a
first metallic material, a second member made of a second metallic
material, and a third member disposed between the first member and
the second member in the axial direction and made of a third
metallic material, and a specific gravity of the third metallic
material may be smaller than a specific gravity of each of the
first and second metallic materials. In this case, the third member
disposed between the first member and the second member allows the
weight of the sprocket to be reduced.
[0031] Each of the first and second metallic materials may be iron,
and the third metallic material may be aluminum.
[0032] The stacked member may include a first member made of a
first metallic material, a second member made of a second metallic
material, and a third member made of a non-metallic material. In
this case, the third member made of a non-metallic material and
disposed between the first member and the second member allows the
weight of the sprocket to be reduced.
[0033] The non-metallic material may contain a resin.
[0034] A straight line that connects a contact position where each
of the rollers comes into contact with the drive side surface when
the chain is driven to the center rotational axis and a line
tangential to the drive side surface in the contact position may
form an angle smaller than or equal to 7 degrees. In this case,
each of the rollers is unlikely to move radially outward on the
drive surface, whereby the chain is unlikely to disengage from the
sprocket.
[0035] A bicycle sprocket according to another aspect of the
invention is engageable with a chain having rollers, The bicycle
sprocket includes a body and at least one tooth portion. The body
is rotatable around a center rotational axis. The at least one
tooth portion is provided along a peripheral portion of the body
and has a front surface, a rear surface that faces away from the
front surface in an axial direction of the center rotational axis,
a drive side surface that connects, on a downstream side in a drive
rotation direction, the front surface and the rear surface to each
other in the axial direction, and a non-drive side surface that
connects, on an upstream side with respect to the drive rotation
direction, the front surface and the rear surface to each other in
the axial direction.
[0036] The at least one tooth portion has a first chamfered portion
in a radially outer portion of one of the front surface and the
rear surface, and the first chamfered portion is on formed that it
is tapered radially outward in the axial direction. A straight line
that connects a contact position where each of the rollers comes
into contact with the drive side surface when the chain is driven
to the center rotational axis and a line tangential to the drive
side surface in the contact position form an angle smaller than or
equal to 7 degrees.
[0037] In the bicycle sprocket, each of the rollers is unlikely to
move radially outward. on the drive surface of the tooth portion,
whereby the chain is unlikely to disengage from the sprocket.
Further, the configuration described above allows an increase in
the chain holding force without alternately differentiating the
axial thickness of the plurality of tooth portions.
[0038] The angle may be smaller than or equal to 3 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Referring now to the attached drawings which form a part of
this original disclosure:
[0040] FIG. 1 is a front view of a sprocket according to a first
embodiment of the invention;
[0041] FIG. 2 is an enlarged plan view of the sprocket;
[0042] FIG. 3 is a front view of a tooth portion of the
sprocket;
[0043] FIG. 4 is a cross-sectional view of the sprocket taken along
a cutting line IV-IV in FIG. 1;
[0044] FIG. 5 is a partial front view of the sprocket and describes
a threshold distance;
[0045] FIG. 6 shows a sprocket according to a second embodiment of
the invention and corresponds to FIG. 2;
[0046] FIG. 7 is a diagrammatic cross-sectional view of a sprocket
according to Variation 1;
[0047] FIG. 8 is a diagrammatic cross-sectional view of a sprocket
according to Variation 2;
[0048] FIG. 9 shows a sprocket according to Variation 3 and
corresponds to FIG. 3.
[0049] FIG. 10 shows a sprocket according to Variation 4 and
corresponds to FIG. 2; and
[0050] FIG. 11 shows a sprocket according to Variation 5 and
corresponds to FIG. 4.
DETAILED DESCRIPTION OF EMBODIMENTS
[0051] Selected embodiments will now be explained with reference to
the drawings. It will be apparent to those skilled in the bicycle
field from this disclosure that the following descriptions of the
embodiments are provided for illustration only and not for the
purpose of limiting the invention as defined by the appended claims
and their equivalents.
First Embodiment
[0052] A sprocket 10 according to a first embodiment of the
invention is a bicycle sprocket engageable with a chain 40 having
rollers 40a, as shown in FIGS. 1 and 2. The sprocket 10 is an
example of a bicycle sprocket. The sprocket 10 is used, for
example, as a front chain wheel of a bicycle. When attached to a
bicycle, the sprocket 10 is typically disposed in a position
slightly more separate from the bicycle than an axially central
position of a rear sprocket assembly formed of a plurality of rear
sprockets. The chain 40 includes rollers 40a, a plurality of pairs
of right and left inner link plates 40b, and a plurality of pairs
of outer link plates 40c, which are connected to the outer side
surfaces of the inner link plates 40b, as shown in FIG. 2. The
plurality of inner link plates 40b are pivotally connected to the
outer link plates 40c with link pins 40d. Each of the rollers 40a
is rotatably attached around the outer circumferential surface of
the corresponding link pin 40d. Since the chain 40 is a known
bicycle chain, no detailed description of the chain 40 will be
made.
[0053] The sprocket 10 includes a body 12, which is rotatable
around a center rotational axis X, and at least one tooth portion
14, which is provided along a peripheral portion of the body 12, as
shown in FIGS. 1 and 2. The body 12 is formed of an annular
plate-shaped member made, for example, of iron, aluminum, titanium,
or any other metal or a carbon fiber reinforced material or any
other non-metallic material. The body 12 has a plurality of crank
attachment portions 12a formed in a radially inner portion, and the
crank. attachment portions 12a are attached to a crank arm (not
shown), for example, with a plurality of screw members. In the
first embodiment, the body 12 is thicker than the tooth portion 14
in the axial direction of the body 12. The body may instead be as
thick as the tooth portion.
[0054] The at least one tooth portion 14 has a front surface 20; a
rear surface 22, which faces away from the front surface 20 in the
axial direction of the center rotational axis X; a drive side
surface 24, which connects, on the downstream side (right side in
FIG. 3) in a drive rotation direction R1, the front surface 20 and
the rear surface 22 to each other in the axial direction; and a
non-drive side surface 26, which connects, on the upstream side
(left side in FIG. 3) in the drive rotation direction R1, the front
surface 20 and the rear surface 22 to each other in the axial
direction, as shown in FIGS. 2, 3, and 4. In the first embodiment,
the tooth portion 14 is located in a plurality of positions, for
example, in 34 positions, The number of tooth portions 14 is not
limited to 34. The tooth portion 14 is made, for example, of iron,
aluminum, or titanium.
[0055] The tooth portion 14 has a first protrusion 28, which
protrudes downstream in the drive rotation direction R1 and located
radially outwardly from a contact position CP, where the drive side
surface 24 comes into contact with each of the rollers 40a when the
chain is driven. A portion of the drive side surface 24 that is
radially outside the first protrusion 28 is formed of an arcuate
surface curved convexly with respect to the first protrusion 28, as
shown in FIG. 3. A portion of the drive side surface 24 that is
radially inside the first protrusion 28 is formed of an arcuate
surface curved concavely with respect to the first protrusion 28.
The first protrusion 28 protrudes downstream in the drive rotation
direction R1 from the contact position CP, where each of the
rollers 40a comes into contact with the drive side surface 24. A
first distance D1 by which the first protrusion 28 protrudes
downstream in the drive rotation direction R1 from the contact
position CP is, for example, greater than or equal to 0.1 mm but
smaller than or equal to 0.5 mm. The first distance D1 is
preferably greater than or equal to 0.2 mm but smaller than or
equal to 0.3 mm, In the first embodiment, the first distance D1 is,
e.g., 0.2 mm. The first distance D1 is defined, by extending the
arc radially outside the first protrusion 28 to a contact circle CL
passing through the contact position CP, as the distance from the
contact position CP to a point of intersection of the arc CC and
the contact circle CL. When the portion of the tooth portion 14
that is radially outside the first protrusion 28 has a straight
line segment instead of the arcuate segment, the first distance D1
may be defined by drawing an imaginary line from the
circumferentially most protruding end of the first protrusion 28
toward the center rotational axis X and measuring the distance to a
point of intersection IP of the imaginary straight line and the
contact circle CL passing through the contact position CP.
Providing the drive side surface 24 with the thus configured first
protrusion 28 prevents movement of each of the rollers 40a of the
chain 40 that is in contact with the drive side surface 24, and the
roller 40a is unlikely to move outward in the radial direction.
Further, the thickness of the plurality of tooth portions 14 in the
axial direction may be slightly smaller than the gap between the
pair of inner links. As a result, the chain holding force can be
increased without alternately differentiating the thickness of the
tooth portions 14 of the sprocket 10.
[0056] A straight line L1, which connects the contact position CP,
where each of the rollers 40a comes into contact with the drive
side surface 24 when the chain is driven, to the center rotational
axis X and a line TL tangential to the drive side surface 24 in the
contact position CP form an angle .alpha. greater than or equal to
-7 degrees but smaller than or equal to 7 degrees. The angle
.alpha. is preferably greater than or equal to -3 degrees but
smaller than or equal to 3 degrees. The angle .alpha. set to fall
within the range described above produces steep inclination of the
drive side surface 24 of the tooth portion 14 in the contact
position CP, and each of the rollers 40a is unlikely to move
radially outward on the drive side surface 24. A tooth tip width W1
of the tooth portion 14 is preferably set to be greater than a
tooth tip width W2 of a tooth portion of related art indicated by
the dotted line as shown in FIG. 3. In this case, the chain 40 is
more unlikely to disengage from the tooth portion 14 of the
sprocket 10.
[0057] The non-drive side surface 26 has no protrusion, such as the
first protrusion 28 on the drive side surface 24, formed thereon.
The non-drive side surface 26 instead has a raised portion 30
formed thereon. The raised portion 30 is formed radially outwardly
from the contact circle CL that is slightly convex toward the
upstream side with respect to the drive rotation direction R1. The
amount of protrusion D5 of the raised portion 30 on the non-drive
side surface 26 is smaller than the amount of protrusion of the
first protrusion on the drive side surface 24 (first distance D1).
In the first embodiment, the drive side surface 24 and the
non-drive side surface 26 are therefore asymmetric with respect to
a straight line L2, which connects the center rotational axis X to
the circumferentially central position of the tooth portion 14. The
shape of the tooth portion 14 described above maintains ease of
engagement between the tooth portion 14 and the chain 40 and
effectively prevents the chain 40 from disengaging from the tooth
portion 14. An angle .beta. between a rise initiation portion of
the raised portion 30 and the straight line L2 ranges, for example,
from 4 degrees to 5 degrees. Further, the raised portion 30 on the
non-drive side surface 26 is not necessarily formed.
[0058] The tooth portion 14 has a first tooth 14a; a second tooth
14b, which is adjacent to the first tooth 14a and upstream of the
first tooth 14a in the drive rotation direction R1; and a third
tooth 14c, which is adjacent to the second tooth 14b and upstream
of the second tooth 14b in the drive rotation direction R1, as
shown in FIG. 5. A second distance D2 between a contact position
CP, where each of the rollers 40a conies into contact with the
drive side surface 24 of the first tooth 14a when the chain is
driven, and a tip downstream position TD, which is the position of
the tip of the third tooth 14c on the most downstream side with
respect to the drive rotation direction, is preferably greater than
or equal to 25.4 mm but smaller than or equal to 27 mm. The second
distance D2 is a threshold distance that allows the chain 40 that
engages with the first tooth 14a to readily engage with the third
tooth 14c. A large second distance D2 makes it difficult for the
chain 40 to engage with the third tooth 14c or is likely to cause
the chain 40 to fall. The second distance D2 is preferably greater
than or equal to 25.4 mm but smatter than or equal to 26.6 mm. The
second distance D2 is set in consideration of the amount of stretch
of the chain 40.
[0059] One of the front surface 20 and the rear surface 22 has a
first chamfered portion 32, which is formed in a radially outer
portion of the tooth portion 14 and tapered radially outward in the
axial direction. The other one of the front surface 20 and the rear
surface 22 has a second chamfered portion 34, which is formed in a
radially outer portion of the tooth portion 14 and tapered radially
outward in the axial direction. In the first embodiment, the front
surface 20 has the first chamfered portion 32, and the rear surface
22 has the second chamfered portion 34. Since the front surface 20
has the first chamfered portion 32, and the rear surface 22 has the
second chamfered portion 34, the chain 40 readily engages with the
tooth portion 14, that is, the third tooth 14c readily engages with
the chain 40 even when the chain is driven with the chain 40
obliquely set.
[0060] The first chamfered portion 32 has a radially outer portion
formed of a first tapered surface 32a, which is indicated by the
straight thick line in a cross-sectional view, and a radially inner
portion formed of a first curved surface 32b, which connects the
first tapered surface 32a to the front surface 20 in an arcuate
shape in a cross-sectional view, as shown in FIG. 4. The second
chamfered portion 34 has a radially outer portion formed of a
second tapered surface 34a, which is indicated by the straight
thick line in a cross-sectional view, and a radially inner portion
formed of a second curved surface 34b, which connects the second
tapered surface 34a to the rear surface 22 in an arcuate shape in a
cross-sectional view. Each of the first chamfered portion 32 and
the second chamfered portion 34 may instead be formed entirely of a
tapered surface or a curved surface. A first connection position
JP1, where the first tapered surface 32a and the first curved
surface 32b are connected to each other, and a second connection
position JP2, where the second tapered surface 34a and the second
curved surface 34b are connected to each other, are located in the
same radially outer position. As described above, since the front
surface 20 has the first chamfered portion 32 and the rear surface
22 has the second chamfered portion 34, the chain 40 readily
engages with the sprocket 10.
[0061] A third distance D3 in the axial direction between a radial
outer periphery end and a radial inner periphery end of the first
chamfered portion 32 is equal to a fourth distance D4 in the axial
direction between a radial outer periphery end and a radial inner
periphery end of the second chamfered portion 34. Each of the third
distance D3 and the fourth distance D4 is preferably greater than
or equal to 0.75 mm but smaller than or equal to 0.95 mm. In the
first embodiment, each of the third distance D3 and the fourth
distance D4 is 0.875 mm. The distance between the front surface 20
and the rear surface 22 of the tooth portion 14 is, for example,
2.1 mm. The thickness of the tip of the tooth portion 14 is
therefore 0.35 mm.
[0062] The second distance D2 described above affects ease of
engagement between the tooth portion 14 and the chain 40 in the
forward rotation of the sprocket 10. When the chain 40 is driven
with the chain 40 so set that the chain 40 is oriented from a rear
sprocket assembly obliquely toward the sprocket 10, which is a
front chain wheel, a shorter second distance D2 allows the tooth
portion 14 of the sprocket 10 to more readily engage with the chain
40. This is because when the first tooth 14a drives the chain 40 in
the state shown in FIG. 5, the axial distance between the tip
downstream position TD, which is the position of the tip of the
third tooth 14c on the most downstream side with respect to the
drive rotation direction, and the chain 40 is small. The second
distance D2 is, however, determined in accordance with the
intervals between the rollers of the chain 40 and preferably has a
length at least twice the intervals between the rollers of the
chain 40. Further, a relatively large value of the third distance
D3 described above allows the tooth portion 14 of the sprocket 10
to readily engage with the chain 40 when the chain is driven, but
too large a value of the third distance D3 is likely to cause the
chain 40 to disengage from the tooth portion 14 when the chain 40
vibrates in the axial direction. In view of the facts described
above, in the first embodiment, the third distance D3 and the
fourth distance D4 are set to be equal to each other.
[0063] In the thus configured sprocket 10, even when the bicycle
travels on a rough road having irregularities, and the chain 40
therefore vibrates and is about to move in a direction that causes
disengagement of the chain 40, the first protrusion 28, which is
provided on the drive side surface 24 of the tooth portion 14 and
protrudes downward in the drive rotation direction R1, restricts
radially outward movement of the chain 40. The chain 40 is
therefore unlikely to result in disengagement even when the bicycle
travels on a rough road. Further, to allow the sprocket 10 to
readily engage with the chain 40 when the sprocket 10 rotates in
the drive direction, the second distance D2 is set at a value
slightly greater than twice the intervals between the links of the
chain 40, As a result, even when the chain 40 is driven with the
chain 40 inclined in the axial direction between the sprocket 10
and the rear sprocket, the chain 40 readily engages with the tooth
portion 14. The chain 40 can therefore be effectively caught even
when the first protrusion 28 is provided. Further, since the third
distance D3 and the fourth distance D4 are set at the same value,
the chain 40 is unlikely to disengage from the tooth portion 14
even when the chain vibrates in the axial direction.
Second Embodiment
[0064] In FIG. 6, a sprocket 110 according to a second embodiment
is a bicycle sprocket engageable with the chain 40 having the
rollers 40a, but the tooth portion 114 differs from the tooth
portion in the first embodiment. The tooth portion 114 has no first
protrusion. The sprocket 110 includes the body 12, which is
rotatable around the center rotational axis X, and at least one
tooth portion 114, as in the first embodiment. In the following
description, the same components as those in the first embodiment
have the same reference characters as those in the first
embodiment, and no description thereof will be made. Components
different from those in the first embodiment have three -digit
reference characters with the last two digits being equal to the
reference characters in t e first embodiment in the
description.
[0065] The at least one tooth portion 114 has the front surface 20;
a rear surface (not shown) that faces away from the front surface
20 in the axial direction of the center rotational axis X; a drive
side surface 124, which connects, on the downstream side (right
side in FIG. 6) in the drive rotation direction R1, the front
surface 20 and the rear surface to each other in the axial
direction; and the non-drive side surface 26, which connects, on
the upstream side (left side in FIG. 6) in the drive rotation
direction R1, the front surface 20 and the rear surface to each
other in the axial direction. In the second embodiment, the tooth
portion 114 is located in a plurality of positions, for example, in
34 positions. The number of tooth portions 114 is not limited to
"34".
[0066] The straight line L1, which connects the contact position
CP, where each of the rollers 40a comes into contact with the drive
side surface 124 when the chain is driven, to the center rotational
axis X and the line TL tangential to the drive side surface 124 in
the contact position CP form the angle .alpha. greater than or
equal to -7 degrees but smaller than or equal to 7 degrees. The
angle .alpha. is preferably greater than or equal to -3 degrees but
smaller than or equal to 3 degrees. In the second embodiment, the
angle .alpha. between the straight line L1 and the tangential line
is set to be greater than the angle .alpha. in the first
embodiment. The angle .alpha. set to fall within the range
described above produces steep inclination of the drive side
surface 124 of the tooth portion 114 in the contact position CP,
and each of the rollers 40a is unlikely to move radially outward on
the drive side surface 124.
[0067] In the second embodiment, the other components are the same
as those in the first embodiment. That is, the sprocket 110
according to the second embodiment has the first chamfered portion
32 and the second chamfered portion 34 as in the first embodiment.
Further, the second distance D2, the third distance D3, and the
fourth distance D4 are set in the same ranges as those in the first
embodiment.
Variations
[0068] Embodiments of the invention have been described above, but
the invention is not limited to the embodiments described above,
and a variety of changes can be made thereto to the extent that the
changes do not depart from the substance of the invention. in
particular, the plurality of embodiments and variations described
herein can be arbitrarily combined with each other as required.
[0069] (a) In the first and second embodiments, the tooth portion
14 (or 114) is made of a single metallic material, but the
invention is not limited thereto. In Variation 1 shown in FIG. 7,
the configuration of a tooth portion 214 of a sprocket 210 differs
from those in the first and second embodiments. That is, the tooth
portion 214 is formed of a stacked member 236 including three
layers stacked on each other in the axial direction of the center
rotational axis X. The stacked member 236 includes a first member
236a, which is made of a first metallic material, a second member
236b, which is made of a second metallic material, and a third
member 236c, which is disposed between the first member 236a and
the second member 236b in the axial direction and made of a third
metallic material. The specific gravity of the third metallic
material is smaller than the specific gravity of each of the first
metallic material and the second metallic material. Each of the
first metallic material and the second metallic material is, for
example, iron, and the third metallic material is, for example,
aluminum. Each of the first metallic material and the second
metallic material is, however, not limited to iron. The third
metallic material is not limited to aluminum.
[0070] In Variation 1, in the tooth portion 214, the first member
236a on the front side and the second member 236b on the rear side,
which come into contact with the chain 40 and hence need to have
sufficient strength, are made of iron, which has large specific
gravity and high strength, whereas the third member 236c, which is
an intermediate layer and does not need to be so strong, is made of
aluminum, which has small specific gravity, whereby the strength of
the sprocket 210 is maintained and the weight thereof is reduced.
The structure of the body as well as the tooth portion 214 can be
the three-layer structure.
[0071] (b) In Variation 2 shown in FIG. 8, a three-layer stacked
member 336 of a tooth portion 314 of a sprocket 310 differs from
that in Variation 1 and includes a first member 336a, which is made
of a first metallic material, a second member 336b, which is made
of a second metallic material, and a third member 336c, which is
made of a non-metallic material. Each of the first metallic
material and the second metallic material is, for example, iron,
and the non-metallic material, for example, contains a resin. Each
of the first metallic material and the second metallic material is
not limited to iron. The non-metallic material is not limited to a
resin.
[0072] In Variation 2, in the tooth portion 314, the first member
336a on the front side and the second member 336b on the rear side,
which come into contact with the chain 40 and hence need to have
sufficient strength, are made of iron, which has high strength,
whereas the third member 336c, which is an intermediate layer and
does not need to be so strong, includes a resin, which has specific
gravity smaller than that of iron, whereby the strength of the
sprocket 310 is maintained and the weight thereof is reduced. The
structure of the body as well as the tooth portion 314 can be the
three-layer structure.
[0073] (c) In the first and second embodiments, the non-drive side
surface 26 has no protrusion that protrudes in the circumferential
direction, but the invention is not limited thereto.
[0074] A tooth portion 414 of a sprocket 410 in Variation 3 shown
in FIG. 9 has a non-drive side surface 426 having a second
protrusion 438, which protrudes in the circumferential direction.
Further a drive side surface 424 has a first protrusion 428. The
first distance D1 associated with the first protrusion 428 is
smaller than the first distance D1 associated with the first
protrusion 28 in the first embodiment and is, for example, 0.15 mm.
Further, the angle .alpha. is, for example, 2 degrees.
[0075] The drive side surface 424 and the non-drive side surface
426 are symmetric with respect to the straight line L2, which
connects the center rotational axis X to the circumferentially
central position of the tooth portion 414. The first protrusion 428
and the second protrusion 438 therefore have the same amount of
protrusion.
[0076] The sprocket 410, which has the second protrusion 438
provided on the non-drive side surface 426, provides a further
increased chain holding force. In FIG. 9 in Variation 3, the drive
side surface 424 has the first protrusion 428, but the drive side
surface may have no first protrusion, as in the second embodiment
shown in FIG. 6.
[0077] (d) In the first and second embodiments and Variations 1 to
3 described above, the tooth portion of the sprocket has a fixed
length in the axial direction (thickness), but the invention is not
limited thereto. In Variation 4 shown in FIG. 10, a tooth portion
514 of a sprocket 510 includes a group of a plurality of first
teeth 514d, each of which has a first chain engagement thickness T1
in the axial direction, and a group of a plurality of second teeth
514e, each of which has a second chain engagement thickness T2,
which is greater than the first chain engagement thickness T1, in
the axial direction, and the total number of tooth portions 514 is
an even number. The first chain engagement thickness T1 of each of
the first teeth 514d is a thickness that allows engagement with the
inner link plates 40b of the chain 40, and the second chain
engagement thickness T2 of each of the second teeth 514e is a
thickness that allows engagement with the outer link plates 40c of
the chain 40 but does not allow the group of second teeth 514e to
engage with the inner link plates 40b. In Variation 5, the group of
first teeth 514d and the group of second teeth 514e, are
alternately arranged in the circumferential direction.
[0078] The first chain engagement thickness T1 of the group of
first teeth 514d is preferably greater than or equal to 1.5 mm but
smaller than or equal to 2.3 mm. The first chain engagement
thickness T1 of the group of first teeth 514d set to fall within
the range described above allows the group of first teeth 514d to
have necessary rigidity and to readily engage with the inner link
plates 40b, The second chain engagement thickness T2 of the group
of second teeth 514e is preferably greater than or equal to 2.5 mm
but smaller than or equal to 5.4 mm, more preferably greater than
or equal to 3.0 mm but smaller than or equal to 4.5 mm. The second
chain engagement thickness T2 of the group of second teeth 514e set
to fall within the range described above prevents the group of
second teeth 514e from engaging with the inner link plates 40b but
allows the group of second teeth 514e to readily engage with the
outer link plates 40c.
[0079] On the other hand, each of the first teeth 514d preferably
has a bar-like (-) shape when viewed from the radially outer side.
Each of the second teeth 514e preferably has a crosshair-like (+)
shape when viewed from the radially outer side. Further, a front
surface 520a of each of the first teeth 514d has a first chamfered
portion 532c, which is so tapered that the axial width of the tooth
gradually decreases radially outward, A rear surface 522a of each
of the first teeth 514d has a second chamfered portion 534c, which
is so tapered that the axial width of the tooth gradually decreases
radially outward. A front surface 520b of each of the second teeth
514e has a first chamfered portion 532d, which is so tapered that
the axial width of the tooth gradually decreases radially outward,
A rear surface 522b of each of the second teeth 514e has a second
chamfered portion 534d, which is so tapered that the axial width of
the tooth gradually decreases radially outward. The chamfered
portions allow the group of first teeth 514d and the group of
second teeth 514e to readily engage with the inner link plates 40b
and the outer link plates 40c. Further, a non-drive side surface
526a of each of the first teeth 514d has no protrusion, whereas a
drive side surface 524a has a first protrusion 528a having the same
configuration as that in the first embodiment, The non-drive side
surface 526b of each of the second teeth 514e has no protrusion,
whereas a drive side surface 524b has first protrusion 528b having
the same configuration as that in the first embodiment.
[0080] The thus configured sprocket 510, in which the alternately
arranged first teeth 514d and second teeth 514e have axial
thicknesses corresponding to the inner link plates 40b and the
outer link plates 40c of the chain 40 respectively, can provide a
further increased chain holding force.
[0081] In Variation 4, the drive side surface 524a of each of the
first teeth 514d has the first protrusion 528a, and the drive side
surface 524b of each of the second teeth 514e has the first
protrusion 528b. Variation 4 is, however, not limited thereto, and
the drive side surfaces may have no first protrusion and have the
same configuration as that of the drive side surface disclosed in
the second embodiment. Further, the non-drive side surfaces 526,
which have no protrusion, may have second protrusions, such as the
second protrusion shown in Variation 3. Moreover, the number of
first teeth may differ from the number of second teeth. In this
case, the number of second teeth may be smaller than the number of
first teeth. It is, however, noted that the group of first teeth
and the group of second teeth need to be so arranged that the group
of first teeth engage with the inner link plates and the outer link
plates, and that the group of second teeth engage only with the
outer link plates.
[0082] (e) In the first embodiment, the third distance D3
associated with the first chamfered portion 32 and the fourth
distance D4 associated with the second chamfered portion 34 are
equal to each other, but the invention is not limited thereto. In
Variation 5 shown in FIG. 11, a radially outer portion of a first
chamfered portion 632. of a tooth portion 614 of a sprocket 610 is
formed of a first tapered surface 632a indicated by a straight
thick line in a cross-sectional view, and a radially inner portion
is formed of a first curved surface 632b, which connects the first
tapered surface 632a to a front surface 620 in an arcuate shape in
a cross-sectional view. A second chamfered portion 634 has a
radially outer portion formed of a second tapered surface 634a,
which is indicated by the straight thick line in a cross-sectional
view, and a radially inner portion formed of a second curved
surface 634b, which connects the second tapered surface 634a to a
rear surface 622 in an arcuate shape in a cross-sectional view.
Each of the first chamfered portion 632 and the second chamfered
portion 634 may be formed entirely of a tapered surface or a curved
surface. The first connection position JP1, where the first tapered
surface 632a and the first curved surface 632b are connected to
each other, is located in a radially outside position than the
second connection position JP2, where the second tapered surface
634a and the second curved surface 634b are connected to each
other. As described above, since the front surface 620 has the
first chamfered portion 632 and the rear surface 622 has the second
chamfered portion 634, the chain 40 readily engages with the
sprocket 610.
[0083] The third distance D3 in the axial direction between a
radial outer periphery end and a radial inner periphery end of the
first chamfered portion 632 differs from the fourth distance D4 in
the axial direction between a radial outer periphery end and a
radial inner periphery end of the second chamfered portion 634. In
Variation 5, the third distance D3 is greater than the fourth
distance D4. The third distance D3 is preferably greater than or
equal to 0.9 mm but smaller than or equal to 1.1 mm, and the fourth
distance D4 is preferably greater than or equal to 0.6 mm but
smaller than or equal to 0.9 mm. In Variation 5, the third distance
D3 is 1 mm, and the fourth distance D4 is 0.75 mm. The distance
between the front surface 620 and the rear surface 622 of the tooth
portion 614 is, for example, 2.1 mm. The thickness of the tip of
the tooth portion 614 is therefore 0.35 mm.
[0084] (f) In the embodiments and the variations described above,
the front surface has a first chamfered portion and the rear
surface has a second chamfered portion. Conversely, the front
surface may have a second chamfered portion and the rear surface
may have a first chamfered portion.
[0085] (g) In the embodiments and the variations described above, a
single sprocket is disclosed, but the invention is not limited
thereto. The invention is also applicable to a sprocket unit having
a plurality of sprockets arranged in the axial direction. in this
case, the sprocket 10 has at least one speed change tooth. Further,
the invention is applicable to all bicycle sprockets including a
rear sprocket having a small number of teeth.
[0086] According to the invention, the first protrusion restricts
movement of a roller of the chain that comes into contact with the
drive side surface, whereby the roller is unlikely to move radially
outward. Further, a plurality of tooth portions can have an axial
thickness slightly smaller than the gap between a pair of inner
links. The configurations described above allow an increase in the
chain holding force without alternately differentiating the
thickness of the tooth portions of the chain. Further, both a
sprocket having an even total number of teeth and a sprocket having
an odd total number of teeth can provide an increased chain holding
force.
[0087] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Thus, the
foregoing descriptions of the embodiments according to the present
invention are provided for illustration only, and not for the
purpose of limiting the invention as defined by the appended claims
and their equivalents.
* * * * *